Exemplary embodiments of the present disclosure relate to a membrane filtration system for removing foreign matter and a membrane bio reactor including the same.
In general, a separation membrane technology is a separation technology using selective permeability of polymer materials. Unlike distillation technology, the membrane separation technology does not cause a phase change and therefore is advantageous in that it can save energy and simplify the process to save space taken up by an apparatus. The separation membrane has been developed around a reverse osmosis membrane and has been applied to ultrafiltration, microfiltration, nanofiltration or the like.
Membrane bio reactors (MBR), which is a membrane filtration system, is a process that uses a separation membrane instead of a sedimentation tank for a final treatment stage of the existing biological treatment processes.
The MBR can increase treatment efficiency of organic substances and nitrogen components or the like by keeping a concentration of microorganisms high in a reactor and can increase efficiency of solid/liquid separation by removing suspended substances, microorganisms or the like using the separation membrane. The MBR may have many advantages of solving the problems of the existing biological treatment processes.
The MBR has a smaller required site area and better treatment efficiency than the existing return activated sludge (RAS) processes, and the use of the MBR is expected to increase to cope with an increase in a water demand due to population growth, urbanization and increasingly stringent water quality regulations.
Unlike a membrane binding treatment system used for subsequent processes of the existing secondary biological treatment facilities, a submerged membrane bio reactor generally refers to a reaction tank that can directly submerge a separation membrane module into a secondary bio reactor to perform a solid/liquid separation, which is devised to achieve a dual effect of raising water quality to a level of advanced sewage treatment simultaneously with performing the solid/liquid separation.
Meanwhile, when the separation membrane module is submerged into the bio reaction tank in most membrane bio reactors (MBR) processes, the separation membrane module corresponding to the treatment capacity is fixedly provided to a separate frame, such that the filtration by the separation membrane is subjected to an upper water-collecting process or a both end water-collecting process according to the form of the separation membrane module to discharge treated water through a filtering pipe.
However, suspended substances or the like attach to the surface of the membrane during the filtration process and block a flow of water and contaminate the membrane, thereby gradually degrading the filtration ability of the membrane bio reactor, increasing a membrane permeation pressure, and creating difficulty in washing the contaminated membrane.
Various application methods of the existing wastewater treatment technologies using a separation membrane have been researched earlier on in Europe and Japan, but have not been developed as realistic application technologies until the early 90's, due to high separation membrane cost, high energy cost or the like and membrane clogging or the like, and therefore have been restrictively applied only to the field of academic research or specific cases.
However, a method for using a separation membrane of a submerged type and a return activated sludge combined type or the like that are utilized as a means for submerging the separation membrane into the activated sludge reaction tank and suppressing the clogging of the separation membrane using an upward water flow caused by air bubbles generated during an aeration process has been proposed since the early 1990's to considerably alleviate the problem of the membrane clogging that was one of the biggest obstacles to the field application of the separation membrane technology.
As described above, conventionally, an air refining method is used to wash the membrane clogging. As one of the air refining methods, a method for removing sludge attached to a membrane by spraying air to an outer wall of a separation membrane in an upward water flow manner has been used.
However, the air refining method has a problem that energy consumption is considerably large because it needs to be performed over the entire range of the separation membrane.